将多数组转换成单数组（java）

Question

is it possible to copy the data from multi[][] to single[]?!?

double multi[][] = { {1.0, 2.0}, {2.11, 204.00, 11.00, 34.00},{66.5,43.3,189.6}};

to

double single [] = {1.0, 2.0, 2.11, 204.00, 11.0, 66.5,43.3,189.6}

Answer 1

With Java 8 you can write:

double[] single = Arrays.stream(multi) //Creates a Stream<double[]>
            .flatMapToDouble(Arrays::stream) //merges the arrays into a DoubleStream
            .toArray(); //collects everything into a double[] array

Answer 2

It's entirely possible. Per @assylias's answer , Java 8 has a very nice solution. If you're not using Java 8, you'll have to do some work by hand. Since the multi elements are different length, The most efficient thing to do would be to use two passes: the first to count how many elements you need in the result and the second to actually copy the elements once you've allocated the array:

int n = 0;
for (int[] elt : multi) {
    n += elt.length;
}
double[] single = new double[n];
n = 0;
for (int[] elt : multi) {
    System.arraycopy(elt, 0, single, n, elt.length);
    n += elt.length;
}

If it is at all possible that an element of multi is null , you'd want to add an appropriate check inside each of the loops.

Answer 3

if you want a logical way..first you have to find the length of multy array content .and then make single [] with that length and add values

double multy[][] = { {1.0, 2.0}, {2.11, 204.00, 11.00, 34.00},{66.5,43.3,189.6}};
int y=0;
for(int x=0;x<multy.length,x++){
    for(int i=0;i<multy[x].length,i++){
       y++;
    }
}
double single [] =new double[y];
y=0;

for(int x=0;x<multy.length,x++){
    for(int i=0;i<multy[x].length,i++){
       y++;
       single[y]==multy[x][i];
    }
}

Answer 4

According to: https://stackoverflow.com/questions/20686499/java-how-to-convert-a-multidimensional-array-to-single-array-easily

ArrayUtils.addAll(array1,array2)